quite correct. Equally as correct is that this is Thailand and there are many ways to skin a cat, I am just pointing out one of the considerations. Once you have the visa transferring in the 65k monthly is certainly a sensible option. Keep large sums of money in a bank account long term is not how I like to manage my money.
Aside from the cost saving of doing it yourself, there is also the consideration of tying up your cash in a bank account for five months etc, unless you can show the 65k a month method. Agent route can make those issues disappear
From what I have read and heard, nobody is being challenged at the airport to travel to Thailand. Possibly because anyone prepared to fly halfway round the world and then stay in ASQ at their own expense for 15 days isn’t a typical tourist. The government are trying to stop people taking unnecessary flights.
I would be extremely surprised if your bank offered a comparable exchange rate to TransferWise. My bank offers free international transfers but they just sting you on the exchange rate instead.